Efficient collection of airborne viruses is crucial for monitoring and preventing the spread of respiratory diseases. The laminar flow water condensation-based growth tube collector (GTC) is a microbial sampler extensively used to collect virus aerosol particles owing to its high recovery of viable viruses. The GTC involves multiple nozzles and eight tubes for sampling flow rates of 6-8 L per minute (LPM). To allow the GTC to operate at a higher flow rate, optimizing GTC performance through investigation of the effects of nozzle-to-nozzle distance is essential. Herein, we examined these effects on the collection efficiency and viability of airborne MS2 viruses collected by the growth-based virus aerosol concentrator (GVC), which is a lab-made single-tubed GTC, at flow rates of up to 6 LPM per tube. The flow interactions between adjacent jets were analyzed by observing the particle deposition patterns. The collection efficiencies of MS2 virus aerosol particles and the enrichment ratio of the GVC increased with increasing nozzle-to-nozzle distance. The infectious virus concentration relative to that in the virus suspension (RIVC) ranged from 0.0093 to 0.095 for 5 min of sampling. At flow rates of 1 and 6 LPM, the RIVC decreased as the nozzle-to-nozzle distance decreased, which may be ascribed to the higher shear stress at shorter nozzle-to-nozzle distances applied to the viruses collected through the cross-flows driven by adjacent jets. These measured RIVC values are much larger than those collected by the BioSampler. These findings can provide important insights into optimizing multiple nozzles in highflow-rate GTCs.

Rapid detection of indoor airborne viruses is critical to prevent the spread of respiratory diseases. Herein, we present sensitive, highly rapid electrochemical measurement of airborne coronaviruses through condensation-based direct impaction onto antibody-immobilized, carbon nanotube-coated porous paper working electrodes (PWEs). Carboxylated carbon nanotubes are drop-cast on paper fibers to make three-dimensional (3D) porous PWEs. These PWEs have higher active surface area-to-volume ratios and electron transfer characteristics than conventional screen-printed electrodes. The limit of detection and detection time of the PWEs for liquid-borne coronaviruses OC43 are 65.7 plaque-forming units (PFU)/mL and 2 min, respectively. The PWEs showed sensitive and rapid detection of whole coronaviruses, which can be ascribed to the 3D porous electrode structure of the PWEs. Moreover, water molecules condense on airborne virus particles during air sampling, and these water-encapsulated virus particles (<4 µm) are impacted on the PWE for direct measurement without virus lysis and elution. The whole detection takes ∼10 min, including air sampling, at virus concentrations of 1.8 and 11.5 PFU/L of air, which can be due to the highly enriching and minimally damaging virus capture on a soft and porous PWE, demonstrating the potential for the rapid and low-cost airborne virus monitoring system.

Growth tube collectors (GTCs) are used to sample virus aerosols because of their superior viable virus recovery among air samplers. However, a major limitation of such samplers is that they operate at low flow rates compared to many inertia-based air samplers. Herein, we demonstrated efficient measurements of airborne MS2 and T3 viruses using a GTC that can implement high flow velocities for higher flow rates per tube, which we refer to as the growth-based virus aerosol concentrator (GVC), via qPCR and the plaque assay technique. The GVC exhibited a flow rate of up to 6 L/min, where the average sampling flow velocity was 5.09 m/s, 22 times higher than those used in the GTCs, for a single tube with a diameter of 5 mm. The count median diameter of the size-increased particles at the exit of the initiator was measured to be 1.44 µm at 6 L/min, considerably smaller than those observed in conventional GTCs. Nevertheless, the measurement of airborne MS2 and T3 viruses using the GVC showed a high concentration (high enrichment ratio of 109,458 at 10-min sampling) of viruses in a sampling medium, with a high viable virus percentage (> 90%) and physical collection efficiency (> 90%) at 6 L/min, which shows the potential for rapid on-site detection of airborne viruses.

Air-transmissible pathogenic viruses, such as influenza viruses and coronaviruses, are some of the most fatal strains and spread rapidly by air, necessitating quick and stable measurements from sample air volumes to prevent further spread of diseases and to take appropriate steps rapidly. Measurements of airborne viruses generally require their collection into liquids or onto solid surfaces, with subsequent hydrosolization and then analysis using the growth method, nucleic-acid-based techniques, or immunoassays. Measurements can also be performed in real time without sampling, where species-specific determination is generally disabled. In this review, we introduce some recent advancements in the measurement of pathogenic airborne viruses. Air sampling and measurement technologies for viral aerosols are reviewed, with special focus on the effects of air sampling on damage to the sampled viruses and their measurements. Measurement of pathogenic airborne viruses is an interdisciplinary research area that requires understanding of both aerosol technology and biotechnology to effectively address the issues. Hence, this review is expected to provide some useful guidelines regarding appropriate air sampling and virus detection methods for particular applications.